<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8" />
        <meta name="viewport" content="width=device-width, initial-scale=1.0" />
        <style>
            /* 清除浏览器默认边距，
使边框和内边距的值包含在元素的width和height内 */
            * {
                margin: 0;
                padding: 0;
                box-sizing: border-box;
            }
            /* 使用flex布局，让内容垂直和水平居中 */
            section {
                /* 相对定位 */
                position: relative;
                overflow: hidden;
                display: flex;
                justify-content: center;
                align-items: center;
                min-height: 100vh;
                /* linear-gradient() 函数用于创建一个表示两种或多种颜色线性渐变的图片 */
                background: linear-gradient(to bottom, #f1f4f9, #dff1ff);
            }
            /* 背景颜色 */
            section .color {
                /* 绝对定位 */
                position: absolute;
                /* 使用filter(滤镜) 属性，给图像设置高斯模糊*/
                filter: blur(200px);
            }
            /* :nth-child(n) 选择器匹配父元素中的第 n 个子元素 */
            section .color:nth-child(1) {
                top: -350px;
                width: 600px;
                height: 600px;
                background: #ff359b;
            }
            section .color:nth-child(2) {
                bottom: -150px;
                left: 100px;
                width: 500px;
                height: 500px;
                background: #fffd87;
            }
            section .color:nth-child(3) {
                bottom: 50px;
                right: 100px;
                width: 500px;
                height: 500px;
                background: #00d2ff;
            }
            .box {
                position: relative;
            }
            /* 背景圆样式 */
            .box .circle {
                position: absolute;
                background: rgba(255, 255, 255, 0.1);
                /* backdrop-filter属性为一个元素后面区域添加模糊效果 */
                backdrop-filter: blur(5px);
                box-shadow: 0 25px 45px rgba(0, 0, 0, 0.1);
                border: 1px solid rgba(255, 255, 255, 0.5);
                border-right: 1px solid rgba(255, 255, 255, 0.2);
                border-bottom: 1px solid rgba(255, 255, 255, 0.2);
                border-radius: 50%;
                /* 使用filter(滤镜) 属性，改变颜色。
    hue-rotate(deg)  给图像应用色相旋转 
    calc() 函数用于动态计算长度值 
    var() 函数调用自定义的CSS属性值x*/
                filter: hue-rotate(calc(var(--x) * 70deg));
                /* 调用动画animate，需要10s完成动画，
    linear表示动画从头到尾的速度是相同的，
    infinite指定动画应该循环播放无限次*/
                animation: animate 10s linear infinite;
                /* 动态计算动画延迟几秒播放 */
                animation-delay: calc(var(--x) * -1s);
            }
            /* 背景圆动画 */
            @keyframes animate {
                0%,
                100% {
                    transform: translateY(-50px);
                }
                50% {
                    transform: translateY(50px);
                }
            }
            .box .circle:nth-child(1) {
                top: -50px;
                right: -60px;
                width: 100px;
                height: 100px;
            }
            .box .circle:nth-child(2) {
                top: 150px;
                left: -100px;
                width: 120px;
                height: 120px;
                z-index: 2;
            }
            .box .circle:nth-child(3) {
                bottom: 50px;
                right: -60px;
                width: 80px;
                height: 80px;
                z-index: 2;
            }
            .box .circle:nth-child(4) {
                bottom: -80px;
                left: 100px;
                width: 60px;
                height: 60px;
            }
            .box .circle:nth-child(5) {
                top: -80px;
                left: 140px;
                width: 60px;
                height: 60px;
            }
            /* 登录框样式 */
            .container {
                position: relative;
                width: 400px;
                min-height: 400px;
                background: rgba(255, 255, 255, 0.1);
                display: flex;
                justify-content: center;
                align-items: center;
                backdrop-filter: blur(5px);
                box-shadow: 0 25px 45px rgba(0, 0, 0, 0.1);
                border: 1px solid rgba(255, 255, 255, 0.5);
                border-right: 1px solid rgba(255, 255, 255, 0.2);
                border-bottom: 1px solid rgba(255, 255, 255, 0.2);
            }
            .form {
                position: relative;
                width: 100%;
                height: 100%;
                padding: 50px;
            }
            /* 登录标题样式 */
            .form h2 {
                position: relative;
                color: #fff;
                font-size: 24px;
                font-weight: 600;
                letter-spacing: 5px;
                margin-bottom: 30px;
                cursor: pointer;
            }
            /* 登录标题的下划线样式 */
            .form h2::before {
                content: "";
                position: absolute;
                left: 0;
                bottom: -10px;
                width: 0px;
                height: 3px;
                background: #fff;
                transition: 0.5s;
            }
            .form h2:hover:before {
                width: 53px;
            }
            .form .inputBox {
                width: 100%;
                margin-top: 20px;
            }
            /* 输入框样式 */
            .form .inputBox input {
                width: 100%;
                padding: 10px 20px;
                background: rgba(255, 255, 255, 0.2);
                outline: none;
                border: none;
                border-radius: 30px;
                border: 1px solid rgba(255, 255, 255, 0.5);
                border-right: 1px solid rgba(255, 255, 255, 0.2);
                border-bottom: 1px solid rgba(255, 255, 255, 0.2);
                font-size: 16px;
                letter-spacing: 1px;
                color: #fff;
                box-shadow: 0 5px 15px rgba(0, 0, 0, 0.05);
            }
            .form .inputBox input::placeholder {
                color: #fff;
            }
            /* 登录按钮样式 */
            .form .inputBox input[type="submit"] {
                background: #fff;
                color: #666;
                max-width: 100px;
                margin-bottom: 20px;
                font-weight: 600;
                cursor: pointer;
            }
            .forget {
                margin-top: 6px;
                color: #fff;
                letter-spacing: 1px;
            }
            .forget a {
                color: #fff;
                font-weight: 600;
                text-decoration: none;
            }
        </style>
        <title>登录界面</title>
    </head>
    <body>
        <section>
            <!-- 背景颜色 -->
            <div class="color"></div>
            <div class="color"></div>
            <div class="color"></div>
            <div class="box">
                <!-- 背景圆 -->
                <div class="circle" style="--x: 0"></div>
                <div class="circle" style="--x: 1"></div>
                <div class="circle" style="--x: 2"></div>
                <div class="circle" style="--x: 3"></div>
                <div class="circle" style="--x: 4"></div>
                <!-- 登录框 -->
                <div class="container">
                    <div class="form">
                        <h2>登录</h2>
                        <form>
                            <div class="inputBox">
                                <input type="text" placeholder="姓名" />
                            </div>
                            <div class="inputBox">
                                <input type="password" placeholder="密码" />
                            </div>
                            <div class="inputBox">
                                <input type="submit" value="登录" />
                            </div>
                            <p class="forget">忘记密码?<a href="#"> 点击这里 </a></p>
                            <p class="forget">没有账户?<a href="#"> 注册 </a></p>
                        </form>
                    </div>
                </div>
            </div>
        </section>
    </body>
</html>
